Automatic washing machines have existed for many years. Conventional automatic washing machines generally include an external cabinet containing a dual tub arrangement in which an inner perforated tub (wash basket) rotates within an outer tub that remains generally stationary. In addition, conventional washing machines include a central column that can rotate independently and act as an agitator.
In a typical wash cycle, clothing is loaded into the wash basket. The outer tub and nested wash basket are filled with wash liquid to a predetermined level and the central column agitates the wash load within the liquid to cleanse the clothing. Once the wash cycle is complete, wash liquid is drained from the outer tub via a drain outlet provided therein. The wash basket then rotates (spins) at a high rate of speed to force wash liquid absorbed by the wash load out of the load, through the wash basket apertures and into the outer tub, from which it is drained via the drain outlet.
The conventional arrangement of a pair of nested wash tubs, and a central agitator rotatable independently of the wash basket, has been a main stay of the industry for decades, serving relatively well in terms of its washing effectiveness and its reliability. This conventional arrangement is not without its shortcomings, however. For example, the requirement of an inner as well as an outer tub increases materials, manufacturing and assembly costs as compared to the case if only a single tub were required. Additionally, the nesting of one tub within another takes up space within the washer cabinet that could otherwise be used to increase load capacity. Likewise, the requirement for two independently rotatable elements, a central agitator and an inner rotatable tub, increases cost and mechanical complexity as compared to the case if both wash agitation and spin action could be accomplished with just a rotatable tub. Finally, the dual tub arrangement requires additional water usage for a given load size, since the space between the outer stationary tub and the inner wash basket must be filled to the desired water level, yet this volume of water does not substantially contact the wash load or aid in the wash action.
Washing machines have been proposed that employ tub rotation as a means for agitating the wash load during the wash cycle. For instance, U.S. Pat. No. 5,271,251 to Kovich et al. discloses a tub with at least one ramp on the floor of an inner wash basket (nested within a stationary outer basket). The ramp is configured to be used in conjunction with a baffle mounted to a sidewall of the wash basket. It is apparent that the baffles are located at least partially below the standing water line on the inner surface of the tub. The bottom ramps are positioned to guide the wash load upward and outward, toward the sidewall of the tub, into engagement with the baffle surfaces that then cause the load to tumble around the baffle.
U.S. Pat. No. 5,878,602 to Kovich et al. discloses baffles spaced about a cylindrical wall portion. No bottom ramps are used in the '602 patent. Rather, a rotatable wash plate is nested in the tub bottom and includes a pair of diametrically opposed ripples or ridges. The wash plate imparts a vertical motion to the load as the wash plate is oscillated.